I have a fog horn on my yacht (supplied when I purchased yacht 3 years ago). It's a single use canister of air with a horn on top. I've never had need to use it but a couple of weeks ago I picked it up and thought it looked pretty basic and felt light weight. I went to Whitworths and the best they had was a similar device with a valve to recharge the canister with air using a pump or compressor to a max of 100 psi. What a dud! At 100 psi I get one 4 second blast and using the pump I get less than 2 seconds. Before I purchased I asked the counter staff how long a fill lasted and they said they didn't know. Sucked in!
I am now looking at 12 Volt truck air horns on eBay that run off a small compressor. Am I making another silly decision? What should I use?
I was looking at all those horns in their catalog a few days ago thinking what a good idea with a hand pump ,
saving money to replace the cartridges , looks like you've saved a lot of guys wasted time and money.
I just remembered I have a tyre inflation adaptor which fits the BC air line from my SCUBA tank. I just tried it and got a 7 second blast from one fill. Still crappy but at least it's fast and easy to refill from my SCUBA tank.
An electric horn with a cig lighter plug and on-off button kept in the locker works wonders.
Use it when the need arises, then put it away again, for years.
Is there something inherently wrong with one of these??
www.whitworths.com.au/plastic-fog-horn
I have heard that a mouth/lung operated fog horn is hard to beat.
It is always ready to use and has zero chance of mechanical unreliability.
I have one of those small canister ones that has a hand pump built in, from WW some years ago.
I have used in anger 
for about 3 hours in Morton Bay in a thick fog, don't know if it was any use unless somebody was sailing. Only boat I saw was a speed boat and I don't think he even saw me, let alone heard me 
Oh, and have used it when manoeuvring on rare occasions. 
Select to expand quoteGlennGee said..
I have heard that a mouth/lung operated fog horn is hard to beat.
It is always ready to use and has zero chance of mechanical unreliability.
The only problem is they work so well they are deafening!, you cant hold it at arms length, you can cover one ear but must sacrifice the other, probably should carry earmuffs with them.
Yep, the inherent problem is that it doesn't leave your hands free to do emergency work at need. Also if you use it to much, you may get light headed from lack of oxygen to the brain, or is that to much oxygen to the brain, oh well it's one or the other.
I like the convenience of a 12 V horn. But given the little use it will get and my preference to minimise weight added to my boat, I will try a mouth operated horn. The one Cisco provided a link to was not in stock in Melbourne. I will see if they can still get it.
Thanks everyone for you thoughts.
